In this Aug. 1 2012, photo, passengers check the departing flights at the Delta Air Lines terminal at JFK International Airport in New York. / Mary Altaffer, AP

by Ben Mutzabaugh, USA TODAY

by Ben Mutzabaugh, USA TODAY

--The number of flight cancellations resulting from Hurricane Sandy is now pushing 14,000, according to the FlightAware flight-tracking service.

And that number -13,785 as of 4:30 p.m. ET - still seems likely to grow over the next day as Sandy moves onshore and heads inland.

So far, FlightAware says Sandy forced the cancellation of 1,300 flights on Sunday and 7,670 so far today (Oct. 29). Tuesday's total currently stands at 4,815 a figure that FlightAware CEO Daniel Baker says "is expected to grow depending on the outcome of the storm, possibly becoming as high as today's number."

Once Tuesday's final cancellation tally is included, it seems to be almost a foregone conclusion that Sandy's toll on flight schedules will top the 14,000 Hurricane Irene-related flight cancellations that were reported over a four-day period in August 2011.

- PREVIOUS UPDATE (from Sunday night): Hurricane Sandy is still more than 24 hours away from making landfall in the U.S. Northeast, but already travelers from from Hawaii to Europe and Asia are feeling the storm's wrath.

Airlines have preemptively canceled nearly 7,000 flights in advance of the storm, affecting not only big U.S. airlines like United and Southwest but also international carriers such as Qatar Airways and Lufthansa.

Flight operations will grind to a trickle - if not an outright halt - tomorrow (Oct. 29) at major airports like New York JFK, Newark Liberty, Philadelphia and Washington Dulles as Sandy nears.

That total of 6,810 cancellations doesn't even include Tuesday, which is likely to see thousands of more cancellations as current forecasts call for the worst of Sandy's effects to linger well into the day.

Once Tuesday's cancellation tally is included, it's possible the total could soar past 10,000 and possibly approach the 14,000 Hurricane Irene-related flight cancellations that were reported over a four-day period in August 2011.

Even by early Sunday afternoon, the nation's two biggest airlines had announced they would suspend flight operations at many of their East Coast airports, including several of their busiest hubs.

United, the nation's biggest carrier, says it will halt all flights at several airports - including at its Newark and Washington Dulles hubs - beginning late tonight and extending at least through mid-day Tuesday.

"Based on the forecast, today (Sunday) we will likely suspend operations scheduled for tonight and tomorrow at several airports in the region," United spokesman Rahsaan Johnson tells Today in the Sky. "Conditions are likely to keep us from operating with an acceptable margin of safety."

"Some of the cancellations begin this evening - as opposed to tomorrow - because we want to ensure we get airplanes out of the path of the storm to minimize disruption for customers outside the region," Rahsaan adds. "We don't want to inconvenience customers flying from, say, Los Angeles to San Francisco, because their airplane is stuck on the East Coast."

Delta, the USA's No. 2 carrier, announced similar plans, saying via Twitter that it would cancel all of its Monday flight at Philadelphia and the three New York City-area airports. That includes two of Delta's hubs - both its domestic hub at New York LaGuardia and its international hub at New York JFK.

American, the third-biggest U.S. airline, also had canceled more than 1,000 flights that had been scheduled to operate during the next three days.

Another major carrier - US Airways - says it is halting all flights at its Philadelphia and Washington Reagan National hubs on Monday. That carrier is also suspending all of its New York-area flights at least through Tuesday morning.

New York-based JetBlue says it will halt all flights by midnight tonight at its main hub at JFK. The carrier says it's making the move so it can "shelter its aircraft in other cities" that are away from Sandy's path. Among the places where JetBlue plans to "shelter" its aircraft: Buffalo, Orlando, Pittsburgh, Barranquilla (Colombia) and even Roswell, N.M. -- a destination JetBlue doesn't normally serve.

The wave of cancellations announced today come even though Sandy is not expected to make landfall until sometime tomorrow (Oct. 29). But Sandy's effects are forecast to be wide-reaching, with tropical storm-forced winds expected to extend from New England to Virginia by Monday evening. That's all but certain to create havoc at major airports that struggle with delays even in relatively mild weather events.

FlightAware, the flight-tracking agency warned that widespread flight disruptions were likely to increase.

"Although most air traffic control towers will close when the wind reaches 60-70 knots, the big factor that will result in early flight disruptions is mass transit shutdowns and the availability of airline and airport staff due to their need to prepare for the storm," FlightAware CEO Daniel Baker says in a statement, noting that New York's mass transit agency plans to halt train service around 7 p.m. this evening.

United Airlines became the first carrier to publicly announce it would begin paring flights ahead of Sandy.

United announced this morning (Oct. 28) it already has started canceling "selected flights to and from mid-Atlantic and northeast airports beginning Sunday evening."

Starting on Monday, United says it will "limit or suspend service" to nearly 30 airports in the region, including at two of its busiest hubs: Newark Liberty and Washington Dulles. United adds that it "expects to resume service on Tuesday with selected cancellations, weather permitting."

FlightAware says it appears United's flights will remain suspended at those airports at least through Tuesday afternoon.

FlightAware CEO Baker predicts other airlines will follow a similar course.

Sandy is expected to make landfall sometime Monday, but the storm's is currently forecast to bring hurricane or tropical storm conditions to a large swatch of the region for up to 72 hours, according to forecasts.

Besides the airlines, Amtrak has already canceled a number of trains, including all of Monday's runs on the popular Northeast Corridor routes between Washington, New York and Boston.

Many customers appear to be taking the airlines up on their offers, though that's prompted a number of complaints via Twitter, Facebook and other social media channels about long hold times on airline reservations lines.

At United, spokesman Rahsaan Johnson tells Today in the Sky that "call volumes are up, which leads to longer wait times, but we've got employees deployed in all our call centers and our at-home agents working."

He suggests customers should first try changing their tickets online.

"Those travelers whose flights are cancelled and who no longer need to travel can delay calling us and apply for a refund after the storm has passed," Johnson adds to Today in the Sky. "That can help to reduce overall volume and wait times for customers who do need to rebook."

Nearly every major U.S. airline has at least one hub or "focus city" among the airports expect to see extreme conditions from Sandy. Several airlines have two, such as United (Newark and Washington Dulles), US Airways (Philadelphia and Washington National) and JetBlue (New York JFK and Boston).

Even a moderate disruption of those airports could affect thousands of flights and tens of thousands of passengers. An outright suspension of flights at a combination of those airports would wreak havoc that could spread throughout the U.S. aviation grid and create a backlog of stranded fliers that takes days to clear.

Even parts of the nation outside Sandy's reach are likely to see flight delays. A flight from Phoenix to Honolulu, for example, could become delayed or canceled if the flight or crew scheduled to fly it gets marooned because of disruptions in the East resulting from Sandy.